How much magnesium is dissolved in seawater?

Seawater is a primary source for the industrial extraction of magnesium, representing an almost inexhaustible supply of the element. While concentrations can vary slightly depending on the source, seawater typically contains approximately 0.13 percent magnesium by weight.1

More precise measurements indicate that the concentration of magnesium in seawater is approximately 1.278 grams per kilogram of seawater. Because the relative proportions of the principal constituents of the oceans remain remarkably constant, this concentration is consistent across most oceanic environments.2